Insights into the Stability of Zeolitic Imidazolate Frameworks in Humid Acidic Environments from First-Principles Calculations

Abstract

Understanding the degradation mechanisms of zeolitic imidazolate frameworks (ZIFs) is crucial to improve their chemical stability and realize their potential industrial applications. Here, we conduct a comprehensive study utilizing dispersion-corrected density functional theory calculations to investigate the chemical stability of bulk ZIFs and their external surfaces under conditions of acid-gas exposure. We examine the influence of steric factors such as topology and ligand functionalization on the relative chemical stability of prototypical ZIFs (ZIF-2 and ZIF-8), including their hypothetical polymorphs. We find that defect formation is more thermodynamically and kinetically favorable at ZIF external surfaces versus the bulk, and that both topology and ligand functionalization impact defect formation. In addition, we provide a detailed mechanism for the reaction of ZIFs with sulfurous and sulfuric acids, of which the latter serves as a catalyst in potential degradation reactions of ZIFs. We also provide information about the adsorption strength of a range of acid gases to defective ZIF structures, which can inform potential strategies to regenerate ZIFs and/or achieve defect engineering in these materials.

Mechanical Properties and Processing Techniques of Bulk Metal–Organic Framework Glasses

“…[6] Several potential applications in membrane based gas separations or as shock absorbers have been suggested. [7][8][9] Their chemical [10] and mechanical [11] properties are, however, less well documented, although the Young's modulus and hardness of single crystal ZIF samples are observed to decrease with increasing internal surface area. [12] One member of this family, ZIF-62 [Zn(Im)1.75(bIm)0.25] (Im imidazolate, C3H3N2 -, bImbenzimidazolate C7H5N2 -), [13,14] has been found to melt at ca 710 K in an argon atmosphere without decomposition.…”

The role of molecular modelling and simulation in the discovery and deployment of metal-organic frameworks for gas storage and separation

“…In subsequent work, Bellarosa and co-workers[373] used Born–Oppenheimer molecular dynamics simulations and showed the degradation of MOF-5 instead occurs through the replacement of the organic linkers by water molecules. Han et al [374] used density functional theory calculations to elucidate the mechanism by which acid gases degrade zeolitic imidazolate frameworks (ZIFs) both inside the pores and at the external surface of a crystallite.…”

The Role of Molecular Modeling & Simulation in the Discovery and Deployment of Metal-Organic Frameworks for Gas Storage and Separation

“…In subsequent work, Bellarosa and co-workers 373 used Born-Oppenheimer molecular dynamics simulations and showed the degradation of MOF-5 instead occurs through the replacement of the organic linkers by water molecules. Han et al 374 used density functional theory calculations to elucidate the mechanism by which acid gases degrade zeolitic imidazolate frameworks (ZIFs) both inside the pores and at the external surface of a crystallite.…”